1. Field of the Invention
This invention relates a liquid laundry detergent which exhibits good detergency even against stubborn oil stains by the application to them in the undiluted form, and permits practical laundering even in soak washing. More specifically, this invention relates to a laundry detergent composition exhibiting both practical detergency and shape-retaining function for silk, wool or delicate clothing, which requires washing even when it is slightly stained, by subjecting it to soak washing. Particularly, this invention pertains to a detergent composition exclusively used for soak washing, which composition exhibits markedly high detergency against oil stains (almost unremovable by washing with water) when applied in the undiluted form and imparts excellent touch feeling compared with the conventional laundry detergent composition.
2. Description of the Related Art
In general, the term "soak washing" conventionally means preliminary washing before washing by a washing machine or by rubbing the laundry with hands, soaking it in a detergent solution which has detergency heightened by the addition of an enzyme. Because the stain cannot be removed sufficiently from the laundry without soaking it in a detergent solution for a long time (ex. overnight), silk or wool garments soaked for such a long time tend to cause shrinkage. The term "soak washing" as used herein means, on the other hand, washing by soaking the laundry in a detergent for a time as short as 10 to 30 minutes and such a short-time soak washing is accompanied with the advantages that it is free from inconvenience, such as shrinkage, of delicate clothing such as silk or wool garments, can accelerate the removal of stain and can finish the laundry with good touch feeling.
In home laundering, clothes are conventionally washed with a detergent mainly composed of an anionic surfactant or nonionic surfactant, followed by softening treatment with a softener mainly composed of a cationic surfactant to impart them with good touch feeling and antistatic capacity. This conventional method is inconvenient, because it requires two separate operations, that is, washing and softening. A washing method using a one-pack type laundry detergent composition in which the above two separate operations are conducted at the same time is disclosed in JP-B-47-4750 (the term "JP-B" as used herein means an "examined published Japanese patent publication") and JP-A-57-126896 (the term "JP-A" as used herein means an "unexamined published Japanese patent application).
The above-described one-pack type composition is composed of a nonionic surfactant or semi-polar surfactant as a main component and as a softener component, a monoalkyl or dialkyl type cationic surfactant containing in its molecule a long-chain saturated group. This system is clear (transparent) at normal temperatures for a while after incorporation. After a long-term storage, however, it separates out insoluble matters and becomes turbid (clouded) or causes precipitation at low temperatures, thereby markedly deteriorating the commodity value. As a result, the one-pack type composition involves a problem in stability in spite of having proper performance in detergency and touch feeling, which makes it difficult to carry out industrial production.
Disclosed in JP-A-4-4298, JP-A-4-153300, U.S. Pat. No. 4,222,905, U.S. Pat. No. 4,259217, U.S. Pat. No. 4,239,659 or the like is a clear neutral liquid detergent having a nonionic surfactant and a cationic surfactant as a basic skeleton. In other words, in the above publications, a clear neutral liquid detergent which has proper detergency, does not impair excellent touch feeling and has excellent storage stability in spite of being a one-pack type detergent is described. Even if the above detergent is employed, delicate clothing, particularly silk or wool garments shrink or lose its original shape after washing by the conventional washing method, more specifically, by washing in a mild water stream in a washing machine or washing by rubbing or pressing the clothing with hands, which considerably deteriorates the commodity value of the clothing. As a washing method to prevent the clothing from shrinkage or to allow the clothing to retain its original shape, a soak washing method is known but for this method, the above detergent is insufficient in detergency and is inferior in the effects for removing the partly marked stains. In addition, a washing method or a detergent which is excellent in tough feeling after washing and shape-retaining function and also in washing function has been demanded. In JP-A-7-54264, JP-A-6-313193, JP-A-8-48993, JP-A-8-48994 and JP-A-8-48995, it is therefore described that an easily water-soluble solvent is incorporated in a laundry detergent composition to make it easier to remove the stubborn oil stains which are hard to be removed by washing in a water system.
In recent days, dry cleaning has caused a serious environmental problem because a solvent such as chlorofluorocarbon (e.g., freon), perchloroethylene (tetrachloroethylene) or petroleum adversely affecting the environment is used in a large amount and in addition, dry cleaning has drawn attentions because of its insufficient removal of water-soluble stain. Delicate clothing, particularly silk or wool garments, should be subjected to dry cleaning for the removal of stubborn oil stains, because ordinary washing method (more specifically, washing in a mild water stream in a washing machine or washing by rubbing or pressing with hands) cannot be adopted for them. It is therefore reported in JP-A-5-51598 that a new dry cleaning solvent using a glycol ether solvent has brought about an improvement in the environmental safety and removal of water-soluble stain. Even when the solvent is used, the removal of water-soluble stain however is not sufficient compared with washing in a water system and this problem has not been overcome sufficiently by the dry cleaning using a solvent.
Under such circumstances, clothes for which the ordinary washing method is not suitable, for example, delicate clothes, particularly silk or wool garments are inevitably washed by the method laying stress on either water-soluble stains or stubborn oil stains.
There is accordingly a demand for a laundry detergent composition which has detergency and touch feeling equal or superior to the conventional soak washing detergent, facilitates the removal of stubborn oil stains, which has so far been removed only by dry cleaning, and is effective for the removal of water-soluble stains and also stubborn oil stains.